Devops Tips and Tricks
#
Check the Status of All Services (upstart) #
In a Linux server that uses upstart, you can quickly check the status of a number of different services by running: `
[sudo] service --status-allThis command will be invoked for all services under the /etc/init.d/ directory.
The - symbol means it isn't running, the + symbol means it is up, and the ? symbol means that it cannot determine the status.
If you want to check the status of something like nginx or apache with more details, just run:
[sudo] service nginx statusCheck the Status of All Services (systemd) #
Severs that utilize systemd can take advantage of the systemctl command. On newe Ubuntu distributions like 16.04 or higher, the service command is just a alias to systemctl. For controlling and checking a service here is what the commands would look like:
sudo systemctl status nginx.service
sudo systemctl start nginx.service
sudo systemctl stop nging.service
sudo systemctl restart nginx.serviceThe files for these services are usually located in /etc/systemd/system and depending on their requriemets they might be in a sub directory from there. You can enable or disable a service like so:
sudo systemctl enable nginx.service
sudo systemctl disable nginx.serviceThis no only keeps it from automatically starting but also can't be started until it's enabled.
Check the Syntax of nginx Files #
The syntax of nginx configuration files can be a bit finicky. On top of that, some nginx server commands can fail silently. Get more confidence by using the following command to check for syntax errors in those files:
$ [sudo] nginx -tIf there is an error, you might see something like this:
$ sudo nginx -t
nginx: [emerg] unexpected ";" in /etc/nginx/nginx.conf:16
nginx: configuration file /etc/nginx/nginx.conf test failedIf all looks good, then you'll see this:
$ sudo nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successfulDetermine the IP Address of a Domain #
The dig (domain information grouper) command can be used to get more information about a domain name. To discover the IP address for a given domain, invoke dig with the domain as an argument.
$ dig jasonkumpf.com
; <<>> DiG 9.10.3-P4-Ubuntu <<>> jasonkumpf.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39939
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 3
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;jasonkumpf.com. IN A
;; ANSWER SECTION:
jasonkumpf.com. 599 IN A 50.63.202.13
;; AUTHORITY SECTION:
. 3199 IN NS i.root-servers.net.
. 3199 IN NS b.root-servers.net.
. 3199 IN NS a.root-servers.net.
. 3199 IN NS e.root-servers.net.
. 3199 IN NS k.root-servers.net.
. 3199 IN NS j.root-servers.net.
. 3199 IN NS g.root-servers.net.
. 3199 IN NS h.root-servers.net.
. 3199 IN NS d.root-servers.net.
. 3199 IN NS c.root-servers.net.
. 3199 IN NS m.root-servers.net.
. 3199 IN NS l.root-servers.net.
. 3199 IN NS f.root-servers.net.
;; ADDITIONAL SECTION:
E.ROOT-SERVERS.net. 30 IN AAAA 2001:500:a8::e
G.ROOT-SERVERS.net. 22938 IN AAAA 2001:500:12::d0d
;; Query time: 101 msec
;; SERVER: 127.0.1.1#53(127.0.1.1)
;; WHEN: Fri Jul 07 18:10:30 EDT 2017
;; MSG SIZE rcvd: 343
The answer section tells me that the IP address for jasonkumpf.com is 50.63.202.13.
See man dig for more details.
Running Out of inode Space #
Unix systems have two types of storage limitations. The first, and more common, is a limitation on physical storage used for storing the contents of files. The second is a limitation on inode space which represents file location and other data.
Though it is uncommon, it is possible to run out of inode space before running out of disk space (run df and df -i to see the levels of each). When this happens, the system will complain that there is No space left on device. Both inode space and disk space are needed to create a new file.
How can this happen? If lots of directories with lots of empty, small, or duplicate files are being created, then the inode space can be used up disproportionately to the amount of respective disk space. You'll need to clean up some of those files before you can continue.